This invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The invention has particular applicability to high areal density magnetic recording media having thin films for longitudinal magnetic recording media, and more particularly, to B2-structured underlayers for use with a cobalt or cobalt alloy based magnetic layer.
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-medium noise ratio (SMNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
Magnetic discs and disc drives provide quick access to vast amounts of stored information. Both flexible and rigid discs are available. Data on the discs is stored in circular tracks and divided into segments within the tracks. Disc drives typically employ one or more discs rotated on a central axis. A magnetic head is positioned over the disc surface to either access or add to the stored information. The heads for disc drives are mounted on a movable arm that carries the head in very close proximity to the disc over the various tracks and segments.
FIG. 1 shows the schematic arrangement of a magnetic disk drive 10 using a rotary actuator. A disk or medium 11 is mounted on a spindle 12 and rotated at a predetermined speed. The rotary actuator comprises an arm 15 to which is coupled a suspension 14. A magnetic head 13 is mounted at the distal end of the suspension 14. The magnetic head 13 is brought into contact with the recording/reproduction surface of the disk 11. The rotary actuator could have several suspensions and multiple magnetic heads to allow for simultaneous recording and reproduction on and from both surfaces of each medium.
An electromagnetic converting portion (not shown) for recording/reproducing information is mounted on the magnetic head 13. The arm 15 has a bobbin portion for holding a driving coil (not shown). A voice coil motor 19 as a kind of linear motor is provided to the other end of the arm 15. The voice motor 19 has the driving coil wound on the bobbin portion of the arm 15 and a magnetic circuit (not shown). The magnetic circuit comprises a permanent magnet and a counter yoke. The magnetic circuit opposes the driving coil to sandwich it. The arm 15 is swingably supported by ball bearings (not shown) provided at the upper and lower portions of a pivot portion 17. The ball bearings provided around the pivot portion 17 are held by a carriage portion (not shown).
A magnetic head support mechanism is controlled by a positioning servo driving system. The positioning servo driving system comprises a feedback control circuit having a head position detection sensor (not shown), a power supply (not shown), and a controller (not shown). When a signal is supplied from the controller to the respective power supplies based on the detection result of the position of the magnetic head 13, the driving coil of the voice coil motor 19 and the piezoelectric element (not shown) of the head portion are driven.
A cross sectional view of a conventional longitudinal recording disk medium is depicted in FIG. 2. A longitudinal recording medium typically comprises a non-magnetic substrate 20 having sequentially deposited on each side thereof an underlayer 21, 21xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 22, 22xe2x80x2, typically comprising a cobalt (Co) -base alloy, and a protective overcoat 23, 23xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 21, 21xe2x80x2, magnetic layer 22, 22xe2x80x2, and protective overcoat 23, 23xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer.
According to the domain theory, a magnetic material is composed of a number of submicroscopic regions called domains. Each domain contains parallel atomic moments and is always magnetized to saturation, but the directions of magnetization of different domains are not necessarily parallel. In the absence of an applied magnetic field, adjacent domains may be oriented randomly in any number of several directions, called the directions of easy magnetization, which depend on the geometry of the crystal. The resultant effect of all these various directions of magnetization may be zero, as is the case with an unmagnetized specimen. When a magnetic field is applied, the domains most nearly parallel to the direction of the applied field grow in size at the expense of the others. This is called boundary displacement of the domains or the domain growth. A further increase in magnetic field causes more domains to rotate and align parallel to the applied field. When the material reaches the point of saturation magnetization, no further domain growth would take place on increasing the strength of the magnetic field.
A magnetic material is said to possess a uniaxial anisotropy when all domains are oriented in the same direction in the material. On the other extreme, a magnetic material is said to be isotropic when all domains are oriented randomly.
Important magnetic properties, such as coercivity (Hc), remanent magnetization (Mr) and coercive squareness (S*), which are crucial to the recording performance of the Co alloy thin film for a fixed composition, depend primarily on its microstructure. For thin film longitudinal magnetic recording media, the desired crystalline structure of the Co and Co alloys is hexagonal close packed (HCP) with uniaxial crystalline anisotropy and a magnetization easy direction along the c-axis is in the plane of the film. The better the in-plane c-axis crystallographic texture, the higher the coercivity of the Co alloy thin film used for longitudinal recording. This is required to achieve a high remanence. For very small grain sizes coercivity increases with increased grain size. Large grains, however, result in greater noise. There is a need to achieve high coercivities without the increase in noise associated with large grains. To achieve a low noise magnetic medium, the Co alloy thin film should have uniform small grains with grain boundaries which can magnetically isolate neighboring grains. This kind of microstructure and crystallographic texture is normally achieved by manipulating the deposition process, by grooving the substrate surface, or most often by the proper use of an underlayer.
The linear recording density can be increased by increasing the Hr of the magnetic recording medium, and by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high-density magnetic hard disk drives, and is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
Underlayers can strongly influence the crystallographic orientation, the grain size and chemical segregation at the Co alloy grain boundaries. Underlayers that have been reported in the literature include Cr, Cr with an additional alloy element X (X=C, Mg, Al, Si, Ti, V, Co, Ni, Cu, Zr, Nb, Mo, La, Ce, Nd, Gd, Th, Dy, Er, Ta, and W), Ti, W, Mo, and NiP. While there would appear to be a number of underlayer materials available, in practice, only a very few work well enough to meet the demands of the industry. Among them, the most often used and the most successful underlayer is pure Cr. For high density recording, in-plane orientation has heretofore been achieved by grain-to-grain epitaxial growth of the HCP Co alloy thin film on a body centered cubic (BCC) Cr underlayer. The polycrystalline Co-based alloy thin film is deposited with its c-axis, the 0002 axis, either parallel to the film plane or with a large component of the c-axis in the film plane. Different Co/Cr epitaxial relationships prevail for different deposition processes. To obtain a good BCC structure which promotes the formation of the HCP structure, the Cr underlayer must be thicker than about 100xc3x85. U.S. Pat. No. 4,652,499 discloses efforts to improve the underlayer by adding vanadium (V) to Cr to change its lattice constant and thereby to promote a better lattice matching between the HCP Co alloys, CoPt or CoPtCr, and the BCC CrV underlayer.
Furthermore, there exists a texture relationship between the underlayer and the magnetic layer. Therefore, the influence of the seedlayer in terms of a texture relationship permeates even into the magnetic layer.
Conventional Cr-alloy underlayers comprise chromium (Cr), vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr.
A conventional longitudinal recording disk medium is prepared by depositing multiple layers of metal films to make a composite film. In sequential order, the multiple layer typically comprises a non-magnetic substrate, one or more underlayers, a magnetic layer, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) alloy magnetic layer is deposited on a chromium or chromium-alloy underlayer.
Conventional methods for manufacturing a longitudinal magnetic recording medium with a glass, glass-ceramic, Al or Alxe2x80x94NiP substrate comprise applying a seedlayer between the substrate and underlayer. A conventional seedlayer seeds the nucleation of a particular crystallographic texture of the underlayer. Conventionally, a seedlayer is the first deposited layer on the non-magnetic substrate. The role of this layer is to texture (alignment) the crystallographic orientation of the subsequent Cr-containing underlayer.
The seedlayer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20xc3x85 thick.
It is recognized that the magnetic properties, such as Hr, Mr, S* and SMNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by one or more underlying layers on which it is deposited.
In co-pending U.S. patent application Ser. No. 09/152,326 filed on Sep. 14, 1998, a magnetic recording medium is disclosed comprising a surface oxidized NiAl seedlayer, and sequentially deposited thereon a Cr-containing underlayer, a CoCrTa intermediate layer and a CoCrPtTa magnetic layer. xe2x80x9cSeedlayer Induced (002) Crystallographic Texture in NiAl Underlayers,xe2x80x9d L.-L. Lee, D. E. Laughlin and D. N. Lambeth, J. AppL. Phys., 79 (8), pp. 4902-4904 (1996), discloses a MgO seedlayer. xe2x80x9cFeAl Underlayers for CoCrPt Thin Film Media,xe2x80x9d L.-L. Lee, D. E. Laughlin and D. N. Lambeth, J. AppL. Phys., 81 (8), pp. 4366-4368 (1997), first reported an FeAl underlayer having a B2 structure.
In order to squeeze as much digital information as possible on a recording disc medium there is a continuing need for improved areal density magnetic recording media exhibiting high coercivity and high SMNR. The need for lighter, smaller and better performing computers with greater storage density demands higher density hard disk media. It is an object of the present invention to meet those demands with a longitudinal magnetic recording media having high coercivity and low noise.
The invention provides a magnetic recording medium for high areal recording density exhibiting low noise, high coercivity. One way of achieving this goal is to produce a magnetic recording medium having a subseedlayer that could alter the structure of the surface upon which a seedlayer is deposited. Preferably, the seedlayer should then be capable of inducing the c axis of a hexagonal crystalline phase (HCP) of a layer above the seedlayer to line predominantly parallel to the magnetic film of the media. The magnetic recording medium of the invention could comprise a substrate, a subseedlayer comprising a Group VIb element, a seedlayer comprised of a material having a B2-ordered crystalline structure, and a magnetic layer preferably formed from a Co or Co alloy film. The substrate could be a disk or a tape.
An underlayer could also be provided, which could comprise of a material having either an A2 structure or a B2- ordered crystalline structure disposed between the seedlayer and the magnetic layer. The A2 phase is preferably Cr or a Cr alloy, such as CrV. The B2 phase is selected from the group consisting of NiAl, AlCo, FeAl, FeTi, CoFe, CoTi, CoHf, CoZr, NiTi, CuBe, CuZn, AlMn, AlRe, AgMg, and Al2FeMn2, and is most preferably FeAl or NiAl.
An embodiment of this invention is a magnetic recording medium, comprising a substrate, a subseedlayer comprising a Group VIb element, a seedlayer comprising a material comprising a B2 structure, and a magnetic layer, in this order. The subseedlayer could further comprise a Group Vb element. The seedlayer could further comprise a (112) laminar texture. In the magnetic recording medium of this invention, a portion of the seedlayer could be oxidized and the medium could further comprise an underlayer comprising a Cr-containing material. The oxidized portion of the seedlayer could contain from about 0.0001 atomic percent oxygen to about 20 atomic percent oxygen, preferably, from about 0.01 atomic percent oxygen to about 0.9 atomic percent oxygen. The oxidized portion of the seedlayer could have a mean grain size diameter of 10 nm or less. In a preferred embodiment, the subseedlayer could be amorphous. The magnetic recording medium could further comprise an intermediate layer interposed between the magnetic layer and the underlayer. In another preferred embodiment, the subseedlayer could be between about 1 nm to 50 nm thick and it could comprise Ta and W or Ni and W; the seedlayer could comprise Ni and Al.
Another embodiment of this invention is a method of manufacturing a magnetic recording medium, comprising depositing a subseedlayer on a substrate; depositing a seedlayer on the subseedlayer and depositing a magnetic layer on the seedlayer, wherein the subseedlayer comprises a Group VIb element and the seedlayer comprises a material comprising a B2 structure.
Another embodiment of this invention is a magnetic recording medium, comprising a seedlayer comprising a material comprising a B2 structure and means for improving a (112) laminar texture of the seedlayer. In this invention, means for improving a (112) laminar texture of the seedlayer is a layer such as a subseedlayer.
As will be realized, this invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from this invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.